I. Field of the Invention
The present invention relates generally to radio communications. More particularly, the present invention relates to switch capacity in a cellular radiotelephone system.
II. Description of the Related Art
Cellular radiotelephone networks provide mobile radiotelephone subscribers access to the landline public switched telephone network (PSTN). FIG. 1 illustrates a typical prior art example of such a radiotelephone network.
This network is comprised of a number of base stations (104-109) that use multiple radio transceivers to communicate with the mobile subscriber (130). The base stations are controlled by base station controllers (101-103) that are coupled to a central switch (100), referred to in the art as the mobile switching center (MSC).
The MSC (100) is a point of access to the PSTN (120). The MSC (100) supervises and controls connections between the PSTN (120) and mobile subscribers (130). Any combination of calls are made possible by the MSC (100): land-to-land, mobile-to-land, land-to-mobile, or mobile-to-mobile. The MSC (100) is well known in the art and is therefore not described further.
This network and its elements are generic to multiple types of radiotelephone systems such as the advanced mobile phone system (AMPS), Global System for Mobile communications (GSM) time division multiple access (TDMA), and code division multiple access (CDMA). These standards are described in greater detail in their respective specifications available from the Electronic Industries Association/Telecommunications Industry Association (EIA/TIA).
In addition to functioning as the interface to the public landline network, the above described switch also controls all of the subsystems required for the cellular system. These subsystems include radio channel units, cell site equipment, mobile subscriber billing, and system operational measurement software that are responsible for determining the operational measurements of the switch. Operational measurements are counters that count, for example, the quantity of calls, hand-offs, and dropped calls.
The switches have a limited operational capacity that determines the maximum number of mobile subscribers that a cellular service provider can service. However, since different operations take different amounts of call processor time, switch capacity cannot be determined strictly by the number of subscribers being handled by the switch.
Currently, statistical trending is used to determine switch capacity. Statistical trending assumes that switch capacity and other measures of switch performance can be predicted based on past history. Subscriber behavior, however, changes significantly over time due to many things. An example of a change in subscriber behavior includes a service operator adding free calling after a certain time that will increase the number of calls through a switch. Also, if the local environment changes due to added relocated roads and office buildings, the number of calls through a switch changes.
Statistical trending does not account for the different real time costs of the numerous call processing and mobility events handled by the switch. Statistical trending also does not take into account the impact of new or changed switch software. There is a previously unknown need for a process that determines cellular switch capacity.